Apparatus for analogue information transfer

ABSTRACT

A method and apparatus for generating second pulse signal from a first pulse signal. The second pulse signal has flanks positioned with a well-defined spacing. The width of the pulses as well as the frequency and phase correspond to the first signal. The apparatus employs a shape generator for generating a shape signal having uniform and well-defined flanks. A frequency generator produces a clock signal wherein the clock and phase correspond to the first pulse signal. The signal generator produces a second pulse signal from the clock signal and the shape signal for use in restoring distorted digital signals to ensure accuracy and signal integrity.

BACKGROUND OF THE INVENTION

The invention relates to an apparatus for analogue information transferwhich comprises a transmit circuit and a receive circuit. The transmitcircuit communicates with the receive circuit through a transmissionmeans, said transmit circuit generating, from a first analogue signal, afirst pulse signal which is transferred to the receive circuit via thetransmission means. The receive circuit generates a second analoguesignal from a second pulse signal. The apparatus finds application in anextremely noisy environment.

Today digital signals are used in an ever increasing number ofelectronic processes. A digital signal consists of a row of pulses whereeach pulse consists of a rising flank and a descending flank, and whereprecisely the spacing between the flanks is decisive for the informationin the signal. The variation in the flanks thus means that pulses withan individual mutual spacing and width are obtained, and in some signalsprecisely these factors are essential to the information in the signal.For the right information to be demodulated from these signals, it isalso important that the flanks are uniform so that their occurrence iswell-defined.

Conversion of analogue signals into digital signals and subsequenttransmission of the digital signals involve the risk that noise pulsesoccur in the signal and that the signal is distorted. This may happene.g. when the digital signal is communicated between two media, or whenthe signals move around in an electronic circuit because ofinterference, time delays or unilinearities in the electronic componentsor in the communications line.

Likewise, capacity between the conductor path or in the communicationsline will attenuate the high frequencies of the pulses more than the lowones and thereby round all the pulses. An analogue value based on adistorted digital signal may be vitiated by serious errors.

As a consequence of the noise pulses it may be difficult to distinguishbetween one of the original pulses and a noise pulse when the digitalsignals are demodulated, and at worst this may mean that the demodulatedsignal is misinterpreted. This misinterpretation may also occur becauseof distortion of the signal.

One way of avoiding the noise pulses is to filter the signal, butparticularly in case of fast signals this filtering causes additionaldistortion of the signal since the filter cannot distinguish between apulse and a noise pulse. When higher order filters are used, thefiltering results in a different type of distortion of the signal as thesignal history repeats itself in the later signal course. Thesedistortions are very unfortunate in the digital signals where theintegrity is of great importance. Integrity in a signal is taken to meana signal where it is important to maintain a great accuracy with respectto the pulse sizes and the mutual positions of the pulses. These factorsare essential to achieve the correct data in connection with decoding ofthe signal.

U.S. Pat. No. 4,027,152 discloses an apparatus for transmitting binarycoded information over a fiber-optic link, which provides a link monitorto indicate whether the fiber optic link is intact and operating. Thebinary coded information is translated into a pulse coded signal whichprovides a positive pulse for positive going transition in the binarysignal and a negative pulse for negative going transition in the binarysignal. In addition a refresh pulse of the same polarity as thepreceding pulse is provided whenever there has been no pulse for apredetermined amount of time.

The use of positive and negative pulses and a neutral level therebetween means that a three level analogue signal has to be transmittedover the optic fiber. Use of thee levels means that the sensitivity tonoise is high because suppressing of noise between the levels is verydifficult. The apparatus is not effective operating in an electricenvironment with a high level of noise.

SUMMARY OF THE INVENTION

The object of the invention is to achieve a precise transfer of ananalogue signal through a transmission means in a noisy environment.

This may be achieved in that the first pulse signal consists of a seriesof coded signals, wherein a first code marks a positive flank, while asecond code marks a negative flank. The receive circuit comprises ashape generator which generates a shape signal with uniform andwell-defined flanks from the second pulse signal, wherein the spacingbetween the flanks approximately corresponds to the spacing between afirst code and a second code in the first pulse signal. Rising andfalling edges of the binary information are aligned with clock markings,where a refresh pulse identical with the preceding information pulse isgenerated, whenever the digital information does not have an edge at therespective clock marking. The receive circuit moreover contains afrequency generator which generates a clock signal on the basis of thecoded pulses of the second pulse signal. The receive circuit alsocontains a signal generator which generates a third pulse signal fromthe clock signal and the shape signal, said third pulse signalgenerating the second analogue signal after D/A demodulation.

This provides a very precise transfer of an analogue signal through atransmission means, where the transferred analogue signal is unique inhaving maintained a very precise phase, and the transfer in general isunique in having a good linearity and a good noise suppression. The useof coding suppresses all other signals which do not live up to thecoding criterion. Further, the coding form involves a power saving inthe signal transfer, including the transmission means, which may be anadvantage e.g. if the transmission means is an optocoupler.

In a particular embodiment of the apparatus, the first pulse signaltransmits a code pulse at fixed intervals. It is hereby possible totransfer a clock signal and code information to the receive circuit,where the clock may be contained in the code.

In a particular embodiment of the apparatus, the first pulse signalcontains a code pulse for a transmit clock signal. It is hereby possibleto transfer code information to the receive circuit, whereby the clocksignal may be restored precisely.

The first pulse signal may contain a first code for marking a positiveflank and a second code for a negative flank, said first and secondcodes being transmitted at fixed intervals in dependence on an originalsignal. It is hereby possible to transfer a square-wave signal.

The original signal may be converted by a code generator into the firstpulse signal, said code generator supplying a clock and performingcoding in dependence on the clock. It is hereby possible to transfer aclock signal and a code signal to the receive circuit, where the clockmay be contained in the code.

Advantageously, the original signal is generated by an analogue todigital modulator. This provides a digital signal which is lesssensitive to noise than the analogue signal.

The original signal may be generated by a sigma delta modulator. Thisprovides a digital signal which is less sensitive to noise than theanalogue signal, and which can simultaneously operate at higherfrequencies.

In a particular embodiment of the apparatus, the receive circuitrecognizes coded pulses, and the original signal is restored on thebasis of the codes. This provides a receive circuit which is capable ofrestoring a square-wave signal.

The receive circuit is capable of restoring the original signal bygenerating a positive state of the signal on the basis of the firstcode, while the second code generates the negative state of the signal.This provides recognition of the original signal on the basis ofwell-defined codes.

The apparatus is capable of restoring the clock from the coded signal inthe receive circuit, said restored clock being used for determining theflanks of the signal. This provides a receive circuit which is capableof generating a clock signal from a coded signal, and which is capableof restoring the original signal from the clock signal and the codesignal.

The apparatus is capable of generating a clock on the basis of thereceived signal in the receive circuit. This provides a receive circuitwhich is capable of generating a clock signal from a received signal.

In a particular embodiment of the apparatus, the receive circuitcontains low-pass (LP) filtering of the second pulse signal. Thisprovides increased noise immunity of a pulse signal.

Advantageously, the apparatus may incorporate a frequency generator witha phase-locked loop. This provides a clock signal, which is synchronouswith the received signal.

The frequency generator can search for the clock within a predeterminedfrequency interval. This provides a clock signal which is synchronouswith the received signal within a given frequency range.

The apparatus may contain the shape generator built as an analogueswitching element, such as e.g. a Smith trigger. This provides a simpleshape generator, which takes up very little space.

The signal generator may be composed of a D flip-flop. This provides asimple signal generator, which takes up very little space.

Advantageously, the second analogue signal is generated in the receivecircuit by means of a digital to analogue demodulator. The secondanalogue signal is hereby restored in a simple manner.

The transmission means may be a transformer, an optocoupler, including alight guide connection or other galvanic separation face. This providesa good separation face between transmit circuit and receive circuit.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be explained more fully below with reference to thefigures, in which

FIG. 1A shows a block diagram which illustrates a problem that is solvedby the present invention.

FIG. 1B shows the signals from the block diagram in 1A.

FIG. 2 shows a block diagram of the restoring principle.

FIG. 3 shows the signals during the restoration.

FIG. 4 shows a particular embodiment of the generator.

FIG. 5 shows a block diagram of an apparatus for analogue informationtransfer.

FIG. 6 shows signals during restoration, associated with the blockdiagram of FIG. 5.

FIG. 7 shows a range of signals, associated with the block diagram ofFIG. 5, using other codes.

DESCRIPTION OF THE INVENTION

An Example of a Problem Solved by the Invention

FIG. 1A shows a block diagram which illustrates an example of a problem,which is solved by the present invention. A digital signal O containinginformation has been generated. This signal is transported, aftergeneration, to a receiver part either via some transmission channels orvia an electrical circuit before it is demodulated. Noise pulses ordistortions of existing pulses may be introduced in the transport phase11. This may be caused by unlinearities in transmission lines,electrical circuits or other obstacles, which the signal has to passbefore it is to be demodulated again. Typically, a filter 13 will beused for removing the noise pulses, which however, distorts the pulsesadditionally. Thus, both the transmission lines and filters contributeto distorting the signal O.

FIG. 1B shows a digital signal A where the pulses have been transportedwithout having been distorted, but where noise pulses 15 have beenintroduced. When this signal is demodulated, it may be difficult todistinguish between a noise pulse 15 and one of the original pulses, inparticular if the original pulses are very fast. Thus, there is a riskthat wrong information is derived from the digital signal A. The noisepulses 15 are thus undesired and are removed by using a filter 13. This,however, has the drawback that particularly the higher frequencies ofthe pulses are attenuated and the signal B is generated. The distortioncauses the flanks of the pulses to lose their well-defined positions.Particularly in case of the signals where the integrity in connectionwith the mutual positions of the flanks—i.e. the pulse width and therelative spacing between the pulses—is of essential importance, it maybe a problem to re-generate the exact data from a signal with distortedpulses. The present invention enables restoration of the original signalO from a distorted signal B, thereby maintaining the integrity.

It should be noted that the present invention may be used for restoringall types of distorted digital signals so that the mutual spacing of theflanks is restored. It is thus not just signals, which have beendistorted because of filtering, but also signals that have beendistorted for other reasons mentioned above.

Finally, it should also be mentioned that it must not necessarily be arestoration that takes place. The present invention may also be used incases where there is a pulse signal and it is desired to generate apulse signal which has been timed from a given clock signal.

General Description of the Invention

FIG. 2 shows a block diagram of the principle in the generator 21,which, from a distorted signal B, generates a signal F where the flanksare well-defined and their mutual spacing has been restored.

The signal B is fed down to a shape generator 23 which shapes thedistorted pulses in B to a shape signal D with uniform well-definedpulse flanks. This shaping results in a shape signal D where therelative position and width of the flanks are not in exactcorrespondence with the original signal O, but where pulses with uniformand well-defined flanks have been generated. This shaping may e.g. takeplace in that, on the basis of some limit values, a unit converts thevalues of the signal into a signal with two different levels.

A frequency generator 25 is used for generating a clock signal which isto be used for timing the shape signal D, so that the mutual spacing ofthe flanks is adapted to the clock which frequency generator generates,from B, a clock signal C containing the timing information from thesignal B.

The information from the clock signal C and the shape signal B iscombined in a signal generator 27 to a signal F containing the sameinformation as O. This may e.g. take place by validating the shapesignal D to the signal F on a clock pulse.

An Example of an Embodiment

FIG. 3 shows a possible embodiment of the generator 21. The shapegenerator 23 is here realized with a Smith trigger 41 which operatesaccording to the following principle: When the signal B exceeds apredetermined value, then the output D switches to state 2, and when Bgets lower than another given value, the output D switches to state 1.Thus, if it is desired to restore the signal O, state 1 and state 2 mustbe the same states between which switching takes place in the signal O.

The frequency generator 25 may be a PLL, also called a phase-lockingloop, which operates in that in a phase comparator 45 it compares thephases of a reference signal B and a clock signal C generated by acontrolled oscillator 47. The control signal for the oscillator 47 isregulated on the basis of the phase difference, thereby generating aclock signal C, which has the same clock and phase as the referencesignal B. Since a phase locking loop is used, a clock signal C isgenerated which, in principle, is insensitive to nose or otherirregularities in the signal B. For the signal to be restored with agiven clock, it is necessary either that the clock is well-representedin the signal or prior knowledge of the clock is available, e.g. fromthe modulation of the signal. To save time and to find precisely thebasic clock again, a minimum frequency and a maximum frequency betweenwhich the frequency generator may move, can be set.

Another way of restoring the clock of the signal might be the use ofFFT.

In one embodiment, the actual signal generation may take place in thatthe clock signal C is delayed by a known size d to the clock signal E.Then, the clock signal E and the shape signal D are applied to a Dflip-flop, thereby generating the signal F. The signal F is generated onthe basis of the clock of the signal E. Each time a signal arrives, withswitching from low to high, the current value is copied from D to F.Thus, signal F is generated wherein the mutual positions of the pulsesand the clock of the signal have been restored, and, thus, theinformation from O (FIG. 1) may now be derived from F (FIGS. 2 and 3).

FIG. 4 shows the signals during the restoration mentioned in theforegoing. It is noted that the shifting d causes restoration of signalF which is phase-shifted by a known size relative to the originalsignal. This, however, is of no significance relative to the informationin the signal, but merely means that the data demodulated from thesignal are delayed relative to O. The shifting d may be determinedaccording to the size of the time distortion in the shape signal D, butis typically very small relative to the overall delay in the rest of thesystems in which the digital signals are used.

FIG. 5 shows an apparatus for analogue information transfer 100 whichconsists of a transmit circuit 101 and a receive circuit 102 that areinterconnected via a transmission means 104. An A/D modulator 107 in thetransmit circuit 101 and a receive circuit 102 that are interconnectedvia a transmission means 104. An A.D. modulator 107 in the transmitcircuit 101 receives a first analogue signal 106 with an analogue curveshape 120 on the input. The A.D modulator 107 converts the firstanalogue signal 106 into an original signal 108 with a digital curveshape 121. The original signal 108 is fed to a code generator 109 whichconverts the original signal 108 into a first pulse signal 110 with thecurve shape 122. The first pulse signal 110 is fed to the receivecircuit 102 via the transmission means 104, so that the receive circuit102 receives a second pulse signal 111 with the curve shape 123. Thesecond pulse signal 111 is fed to a frequency generator 113 and a shapegenerator 112. The shape generator 112 generates a shape signal 114which is fed to a signal generator 116. The frequency generator 113generates a clock signal 115 which is fed to the signal generator 116.The signal generator 116 generates a third pulse signal 117 which is fedto a D/A demodulator 118. The D/A modulator 118 generates a secondanalogue signal 119 with an analogue curve shape 124 which is fed to theoutput.

FIG. 6 shows signals during restoration, associated with an apparatusfor analogue information transfer 100. A first analogue signal 106 isvisible on the first curve. The associated original signal 108 isvisible on the second curve. The associated first pulse signal 110 isvisible on the third curve. Then, marking of the clock for the signalsin the transmit circuit 101 is visible. The second pulse signal 111 isvisible on the fourth curve, corresponding to the first pulse signal 110after reception in the receive circuit 102. A filtered signalcorresponding to the second pulse signal 111 after filtering is visibleon the fifth curve. The associated shape signal 114 is visible on thesixth curve, phase-shifted relative to the preceding signals, but withthe phase between the pulses maintained. Then, marking of the clock inthe receive circuit 102 corresponding to the clock signal 115 isvisible. The third pulse signal 117 is visible on the seventh curve. Thesecond analogue signal 119 is visible on the eight curve.

FIG. 7 shows a range of signals associated with an apparatus foranalogue information transfer 100, but using other types of codes. Theoriginal signal 108 is visible on the first curve. The associated firstpulse 110 using the coding shape 201 is visible on the second curve. Thefirst pulse signal 110 is visible on the third curve if the coding shapeis used instead. The first pulse signal 110 is visible on the fourthcurve if the coding shape 203 is used instead. Then marking of the clockof the signals in the transmit circuit 101 is visible.

What is claimed is:
 1. An apparatus for analogue information transferwhich comprises a transmit circuit and a receive circuit, said transmitcircuit communicating with the receive circuit through a transmissionmeans, transmit circuit generating, from a first analogue signal, afirst pulse signal which is transferred to the receive circuit via thetransmission means, said receive circuit generating a second analoguesignal from a second pulse signal, wherein the first pulse signalconsists of a series of coded pulses, wherein a first code marks apositive flank, while a second code marks a negative flank, wherein thereceive circuit comprises a shape generator which generates a shapesignal with uniform and well-defined flanks from the second pulsesignal, wherein the spacing between flanks approximately corresponds tothe spacing between a first code and a second code in the first pulsesignal, where rising and falling edges of the binary information arealigned with clock markings, where a refresh pulse identical with thepreceding information pulse is generated, wherever the digitalinformation does not have an edge at the respective clock marking, andwherein the receive circuit moreover contains a frequency generatorwhich generates a clock sign on the basis of the coded pulses of thesecond and pulse signal, wherein a signal generator from a third pulsesignal from the clock signal and the shape signal, said third pulsesignal generating the second analogue signal after D/A demodulation. 2.An apparatus according to claim 1, wherein the first pulse signaltransmits a code pulse at fixed intervals.
 3. An apparatus according toclaim 1, wherein the first pulse signal contains a code pulse for atransmit clock signal.
 4. An apparatus according to claim 1, wherein thefirst pulse signal contains a fist code for marking a positive flank anda second code for a negative flank, said first and second codes beingtransmitted at first intervals in dependence on an original signal. 5.An apparatus according to claim 1, wherein the original signal isconverted by a code generator into the first pulse signal, said codegenerator supplying a clock and performing coding in dependence on theclock.
 6. An apparatus according to claim 1, wherein the original signalis generated by an analogue to digital modulator.
 7. An apparatusaccording to claim 1, wherein the original signal is generated by asigma delta modulator.
 8. An apparatus according to claim 1, wherein thereceive circuit recognizes coded pulses and restores the original signalon the basis of the codes.
 9. An apparatus according to claim 1, whereinthe receive circuit restores the original signal by generating apositive state of the signal on the basis of the first code, while thesecond code generates the negative state of the signal.
 10. An apparatusaccording to claim 1, wherein the receive circuit restores the clockfrom the coded signal, said restored clock being used for determiningthe flanks of the signal.
 11. An apparatus according to claim 1, whereinthe receive circuit generates a clock on the basis of the receivedsignal.
 12. An apparatus according to claim 1, wherein the receivecircuit contains a low-pass (LP) filtering of the second pulse signal.13. An apparatus according to claim 1, wherein the frequency generatoris built as a phase-locked loop.
 14. An apparatus according to claim 1,wherein the frequency generator searches for the clock within apredetermined frequency interval.
 15. An apparatus according go claim 1,wherein the shape generator is built as an analogue switching element,such as e.g. a Smith trigger.
 16. An apparatus according to claim 1,wherein the signal generator is composed of a D flip-flop.
 17. Anapparatus according to claim 1, wherein the second analogue signal inthe receive circuit is generated by means of a digital to analoguedemodulator.